How can we help people to reach their full intelligence potential and to what degree is intelligence influenced by the environment and heredity?

-- Jerry Lee (jerrylhl@hotmail.com), October 26, 2003

Answers

This has been discussed many times before on this list. Have a look at the questions in the "Testing" category. Although the heredity folks say that intelligence is about 70%-80% genetic, there has been some very recent research (like, within the past month or two) showing that the correlations are much lower for people of lower socioeconomic status (SES) and higher for those of middle and upper SES. If true, the reason is likely to be that environment can do quite a lot to improve one's intelligence, up to a certain point. Once one has all the "essentials" in abundant supply (i.e., is "middle class"), adding more can't improve things much further and the contribution of genetic endownment tends to overwhelm the contribution of *more* good food, enriched play areas, ready access to good educational materials, etc.

Having said that, I'll repeat what I've said before, which is that thinking of the contributions of environment and heredity as additive (e.g., 70% one, 30% the other) is a hopeless oversimplification of the situation. They interact in far more complex ways than can be adequately captured by percentages. Consider PKU. "How much" is heredity and "how much" environment? If there were no phenylalanine in the environment, there would be *no* PKU syndrome. If there were no genetic structure making phenyalanine toxic, there would be no PKU syndrome either. That sounds more llike a *multiplicative* relationship than an additive one (viz., if either factor is 0, the total is 0). Intelligence is, of course, a much more complicated matter than PKU. Additive percentages don't do it justice.

-- Christopher Green (christo@yorku.ca), October 26, 2003.

The long standing controversy about the relative contribution of genetic factors(nature)verses environmental factors (nuture)has been prominent in the debate about IQ differences.In general it is now widely accepted that each makes a considerable contribution and that the two interact.Buchard and McGue(1981) produced a summary of a large number of studies conducted worldwide.They found the ratio to be in the region of 50/50.Intelligence means different things to different people.So this debate will go on forever.

-- Sydney George Judge (Sydey@judge9163.fsnet.co.uk), November 02, 2003.

My understanding is that research with twins, both fraternal and identical, adopted children etc. shows that intelligence is about 50 per cent inherited and the other 50 per cent is NOT shared environment, or nurture as it is called. The other 50 percent might have something to do with unique experience, or with chance, or with ...? The point being that nurture (shared environment) contributes very very little to intelligence.

-- Douglas Young (goyoung@d1.dion.ne.jp), November 12, 2003.

In response to Douglas Young:
The problem with the classics twins studies is that the environments in which the identical twins were brought up in were not that different from each other. Adoption agencies tend to give children to homes of a relatively narrow classgroup, etc. As a result, the studies may have suffered from a "restriction of range" problem which artifically depressed the correlation coefficients.

-- Christopher Green (cgreen@chass.utoronto.ca), November 12, 2003.